Should You Replace the Tandem Pump Shaft on a Case 1840 Skid Steer

[MikePhua]

The Case 1840 and Its Hydraulic Architecture
The Case 1840 skid steer loader, introduced in the early 1990s by Case Corporation, quickly became a favorite among contractors and landscapers for its reliability and mechanical simplicity. With a rated operating capacity of around 1,400 pounds and a 51-horsepower diesel engine, the 1840 was built to handle tough jobs with minimal electronics and robust hydraulics. Thousands of units were sold across North America, and many remain in service today due to their rebuildable components and widespread parts availability.
At the heart of the machine’s hydraulic system is a tandem pump assembly, which powers both the drive motors and auxiliary functions. The pump is driven by a splined shaft connected to the engine via a coupler. This shaft and coupler are subject to wear over time, especially if the rubber isolators fail or if misalignment occurs.
Assessing Shaft Wear and Coupler Damage
When inspecting the tandem pump shaft, the key concern is spline wear. Splines are the ridges or teeth on the shaft that engage with the coupler. Over time, these splines can become rounded or sharp-edged, indicating material loss. If the splines are visibly worn but not yet sharp, the shaft may still function—but it’s nearing the end of its service life.
Terminology Explained

• Splined Shaft: A shaft with ridges that fit into a matching coupler to transmit torque.
  
• Coupler: A mechanical connector between the engine and pump, often with rubber isolators to absorb vibration.
  
• Mounting Rubbers: Rubber bushings that cushion the coupler and reduce shock loads.
  

When to Replace the Shaft
Replacement should be considered under the following conditions:

• Splines are visibly sharp or uneven This indicates advanced wear and risk of slippage or failure.
  
• Coupler shows excessive play or damage A worn shaft can damage a new coupler quickly, wasting parts and labor.
  
• Rubbers are missing or degraded Without proper isolation, the shaft experiences higher stress and accelerates wear.
  
• Pump removal is already planned If the pump is being removed for other repairs, replacing the shaft is more cost-effective during disassembly.
  

Recommended Repair Strategy

• Order OEM or high-quality aftermarket coupler kits These typically include bolts, rubbers, and the coupler body.
  
• Inspect shaft splines with calipers or spline gauges Compare measurements to factory specs if available.
  
• Use alignment tools during reinstallation Misalignment can cause premature wear on the new shaft and coupler.
  
• Flush hydraulic fluid after reassembly Metal particles from worn splines may contaminate the system.
  

A Story from the Field
In Missouri, a technician tore down a Case 1840 and found all eight mounting rubbers missing from the coupler. The splines on the pump shaft were worn but not yet sharp. He replaced the coupler and rubbers but left the shaft in place. Six months later, the new coupler began to fail due to uneven spline engagement. On the second repair, he replaced the shaft and coupler together, and the machine ran trouble-free for years.
Preventive Maintenance Tips

• Inspect coupler and shaft every 1,000 hours
  
• Replace mounting rubbers proactively every 2,000 hours
  
• Check for vibration or noise during startup
  
• Use anti-seize compound on bolts to ease future disassembly
  

Conclusion
Replacing the tandem pump shaft on a Case 1840 is a judgment call based on spline condition, coupler wear, and overall system health. If the splines show moderate wear and the pump is already being serviced, replacement is a smart investment. With proper alignment and quality parts, the hydraulic system can be restored to full performance, extending the life of this dependable skid steer.